Automatic grinder control



Oct. 20, 1931.

RUPPIQRECHT 1,328,622

AUTOMATIC GRINDER CONTROL Filed May 15; 1921 MR l-MT MD M I" MIMI/NE No. I,

GR IVU swim OF Ma LIFT/w w 40mm m mMmz/m: No.2.

mm: W m M46421! w. 2

Inventor:

Konv'ad Ru'pprecht His Attorney.

Patented Oct. 20, 1931 UNITED STATES PATENT OFFICE KONRALD RUPPRECHT, OF BERLIN, GERMANY, ASSIGNOR T0 GENERAL ELECTRIC 00M- PANY, A CORPORATION OF NEW YORK aurouarrc GRINDER con'rnon Application filed May 13, 1927, Serial No. 191,244, and in Germany June 8, 1926'.

It is already known how to regulate the pressure on the wood when several grinders load of the grinder motor is maintained in all circumstances, for example, even when one of the grinders or when one of the feed devices is put out of operation. In such a case the pressure on the stone remaining in operation is increased to such an extent that the grinder motor remains normally loaded. In this connection, however, there is the disadvantage that the grinding is too coarse and thus difliculties may occur in the further working of the pulp.

In order to obtain a grinding of constantly equal value, the grinder drive according to the invention is to have such a regulating device that on the failure of one grinder or its feed mechanism, the pressure-on the stone of the grinder still in operation remains unchanged. Naturally in this case an overloading of the grinder motor must be taken into account.

This regulating device can now be con structed in so simple a manner that on the stopping of the grinder or when the feed arrangement is cut out of operation, the stones are automatically unloaded and the-feed motors are only again switched in when the grinding operation is resumed. In this manner the stones are spared. At the same. time the advantage is afforded that the starting of the grinder motor is facilitated and the starting current strength is reduced, so that fewer requirements are made in respect to the con'- struction of the grinder motors. This is of.

special importance for the use of asynchronously starting synchronous motors whose construction requires different designs according to the value of the starting moment desired. If the drive of the wood feed arrangements is effected through a chain gear, as will be mostly the case in practice, then the unloading of the grinders cannot be effected by the running back of the feed motors, because the chain transmission is only arranged for a definite working direction. An effective unloading can therefore only be made by,"

raising the magazine of the grinder.

'A constructional example of the subject of the application is represented in the accompanyi ng drawing. M- designates the grinder motor which is coupled with two. grind stones which are not represented. The feed motors M and M which are constructed as single phase alternating current commutator motors, for example, as repulsion-motors, serve for the drive of the wood feed arrangements. The lifting motors M and M serve for lowering and raising'the magazines for the wood being ground. These motors are suitably arranged as three-phase asynchronous motors with short-circuit rotor. They can also be three-phase or direct current motors without the effect of the lifting arrangements being impaired. The commutator motors M and M are connected in] paralleland are fed in common by two single-phase transformers lo.- cated in the line of the grinder niotora voltage transformer T and a current transform- I or T -in well known differential connection through the circuit controllers or contactors S and S The number of secondary windings of the transformer T can be varied in dependence on the number of .grinders in operation, so that the secondary voltage of this transformer can be maintained at the same value independently of the number of grinders actually in operation. This is only transformer T can, also be set up with the normalnumbenof turns for operating both grinders and when operating only one grinder a booster transformer T can be connected in series with transformer T The effect of the current transformer T T is more complete if a choke coil D, D is connected 'in parallel. It is suitable to provide the transformers T T as well as the choke coils D, D with taps.

In order to vary the effective number of turns of the transformers T T in the manner required when changing over from operatlon with one feed motor to that with two main contact 13 of contactor S If only one of the feed motors is to be operated then the other is cut out by opening the associated control switch H or 11 If. for example, feed motor M is cut out, then the circuit of the feed motor M working alone is as follows: Main contact 14 of conta ctor S and contact 15 of contactor S connections 16-17 of the transformer windings T and T windings of the feed motor M main contact 12 of contactor S and the secondary winding of the transformer T If protective device S is cut out and-S only is closed then the course of the circuit of feed motor M is through a similar circuit which is readily traced.

The automatic change over switches or contactors U and U for the lifting motors M and M according to the invention, are interconnected with the contactors S and S of the feed motors in such a manner that the -contactor S must be in its open position, that shown, in order for the contactor U to be energized and closed to energize the lifting motor M in the lifting direction. This is accomplished by the auxiliary switch 18 associated with contactor S which is closed only when contactor S is in its open position. The upper limit switch ofmagazine No. 1 automatically opens when magazine No. 1 is raised to its predetermined upper limit, and thus deenerg'izes the motor M Also, the magazine No. 1 must be in its predetermined lower position before the feed motor M can be energized to feed the wood to the stone associated with this magazine. This is controlled by the right hand contact of the lower limit switch of magazine No. 1 which is closed only when the magazine has been lowered to the predetermined position. This lower limit switch automatically deenergizes motor M to stop the lowering of the magazine at the predetermined position. A similar arrangement is provided for the control of the feed motor M and the magazine lifting and lowering motor M On the other hand the feed motors cannot be switched in before the a: press boxes are again lowered. The push has been previously closed and the grinder motor M has been started, so that the control current interlocking contacts 19 at the oil switch and similar contacts 20 of the starter A are closed. It is also assumed that the disconnecting switches 21 and 22 of motors M and M, are closed.

In the operation of the system as heretofore described, the disconnecting switches 21 and 22 for the motors M and M are closed whereby the control of these motors can be effected through their respective contactors U and U. These motors are then started up by means of the push buttons E and E respectively and operate in a direction to lower the magazines, the motors being stopped with the magazines in their lowermost positions by means of the lower limit switches.

The grinder motor M is now started by closing the oil switch 0 which also closes the interlocked contacts 19 in the operating coil circuits for the contactors S and S The grinder motor M is accelerated to full speed by moving the starting device A to short cir- .cuit the resistance in the secondary circuit of the grinder motor. and when the resistance has been short circuited the starting device closes a circuit between the contacts 20 which completes the circuit for the operating coils of the contactors S and S through the right hand contacts of the lower limit switches of the two magazines, which contacts were closed when the magazines were lowered. The closing of the contactors S and S start the feed motors M and M which operate to feed the wood to the grinder stones.

By opening the manually operated switches H and H either one of the contactors S and S can be opened to deenergize the respective feed motor. When this occurs the corresponding magazine motor M or M is automatically started up in a direction to lift the magazine. This is effected by means of the auxiliary switch 18 connected with each of the contactors S and S2, which switch is closed when the contactor opens thereby operating the corresponding magazine motor contactor U or U in a direction to cause the motor to raise the magazine. When the magazine has been raised to its uppermost position the motor is stopped by the limit switch associated with the magazine. this arrangement it will be observed that when either one'of the feed motors is deenergized the corresponding magazine is au- With ' the corresponding stone.

' first lowered by The raising of the magazine opens the right hand contact of its lower limit switch which in turn opens the circuit for the operating coil for the contactor S or S of the feed motor, thus preventing the restarting of the feed motor until the magazine has been ressing the appropriate button E or E. en the button is pressed to again lower the magazine with the grinder motor operating, the corresponding feed motor is automatically restarted by the closing of the ri ht hand contacts of the lower limit switch 0 the magazine.

The following advantages are obtained through this mutual interlocking and automat1c connection:

(1) All switching processes take place in the right order.

(2) The grinder motor on starting is only loaded. with the stones running light.

(3) The connecting of the feed motor is only positively and automatically effected after the lowering of the associated magazines.

(4) The connection of the current transformer T corresponds to the-actual operating condition of the grinders.

(5) On switching off the feed motors the magazines are automatically lifted.

(6) On releasing the oil switch 0 the feed motors are automatically disconnected and the grinders are unloaded.

When work is to be done. by only one of the two grinders, then the feed motor and the lifting motor of the other grinder can be cut out bymeans of the switches H and H or H and H The arrangement described above can also be used for installations in which the grinder motor M drives more than two 'or only one grind stone. The arrangement is alsoeasily adaptable for the case where the grinder has several magazines which are fed by a corresponding number of feed motors.

What I claim as new and desire "to secure by Letters Patent of the United States, is:

1. In combination, in a system of control for a grinder, a motor for operating feed mechanismfor the grinder, a second motor for raising the grinder magaz ne, and electrical connections throughwhich said second motor is automatically energized to raise the zine, and electrical connections through 3. In combination in a system of control magazine when gized.

2. In combination in a system of control for a grinder a motor for operating feed mechanism for the grinder, a second motor for raising and lowering the grinder magasaid feed motor is deenerwhich said second motor is automatically deenergized and 'said feed motor is automa'tically energized when the magazine has been lowered to a predetermined position.

for a grinder, a motor for operating feed mechanism for the grinder, a second motor "for raising and lowering the grinder magazine, controlling means for said motors, and electrical connections through which said second motor is automatically energized to raise the magazine when said feed motor is deenergized, and said second motor is automatically deenergized and said feed motor is automatically energized when the magazine has been lowered to a predetermined position.

4. In combination in a system of control for a plural stone grinder, a grinder motor for a plural stone grinder, a grinder motor for operating the grind stones, a separate motor for operating an associated feed mechanism for each of said stones, switching mechanism for selectively controlling the energization of said motors, means responsive to the current supplied to said grinder motor for regulating the operation of said feed mo tor, and means operated by said switching J mechanism for adjusting said regulating means in dependence on the number of said feed motors in operation.

In witness whereof, I have hereunto set In hand this 25th day of April, 1927. KONRAD RUPPRECHT. 

